A226283 a(n) = [n/2]!*[(n+1)/2]!*C([n/2],2)*C([(n+1)/2],2).

0, 0, 0, 4, 36, 324, 2592, 20736, 172800, 1440000, 12960000, 116640000, 1143072000, 11202105600, 119489126400, 1274550681600, 14748372172800, 170659735142400, 2133246689280000, 26665583616000000, 358503957504000000, 4819886539776000000, 69406366172774400000

Offset

1,4

Comments

Number of permutations of n elements with 4 odd displacements.

Column 3 of A226288.

Column k=4 of A145893, a diagonal of A145894. - Alois P. Heinz, May 29 2014

Links

R. H. Hardin, Table of n, a(n) for n = 1..210

Mathematica

a[n_]:=(Floor[n/2])!(Floor[(n+1)/2])!Binomial[Floor[n/2], 2]Binomial[Floor[(n+1)/2], 2]; Array[a, 23] (* Stefano Spezia, Jul 12 2024 *)

Crossrefs

Cf. A145893, A145894, A226288.

Sequence in context: A279581 A093186 A000765 * A270473 A374388 A288269

Adjacent sequences: A226280 A226281 A226282 * A226284 A226285 A226286

Keyword

nonn

Author

R. H. Hardin, connection of formula with combinatoric problem via N. J. A. Sloane in the Sequence Fans Mailing List, Jun 02 2013

Status

approved